FIG 5.

Essential role for exogenous protease in CoV entry. (a) Surface-bound host-cell protease mediates clade 1 RBD entry following ACE2 binding. (b) Data from this study exclude the possibility that trypsin may act on the receptor and support the possibility (c) that trypsin cleaves viral spike during entry. (d) Trypsin-dependent, bat-derived betacoronaviruses contain deletions in their RBDs compared to closely related coronaviruses with known receptors. (e) Alphacoronaviruses with known receptors also differ from a subset of closely related but trypsin-dependent, animal viruses with deletions or insertions in their RBDs.